Why do the Gov't barrels profiles have so many contours?

[JonF 79]

Or in other words, why does the profile diameter vary all along the entire shank especially in the M4 variants? Is it for attachment of standardized barrel hardware or is there something to do with harmonics perhaps?

 

[GRIZ 3,369]

attachment of standardized barrel hardware or is there something to do with harmonics perhaps

 

It's a bit of both.

[Maksim 1,504]

I thought it was to put more metal where they can to help in cooling in sustained fire.

[Shane45 807]

Its for mounting of the M203....

[Bob B 103]

You guys are all way off. It's so the manufacturer can charge more.